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As a control, the team also put two identical smartphones in a silent room.

Several popular apps, including Faecbook, Instagram, Google Chrome, Snapchat, YouTube and Amazon were kept open during the experiment.

At the end of the 30 minutes, the researchers looked at the ads related to pet food on each app and webpage, and also looked at the data consumption and battery usage of the smartphones.

The results revealed that the activity and adverts on the smartphones was almost identical in the audio room and the silent room.

Speaking to the BBC , James Mack, systems engineer at Wandera, said: “We observed that the data from our tests is much lower than the virtual assistant data over the 30-minute time period, which suggests that the constant recording of conversations and uploading to the cloud is not happening on any of these tested apps.

"If it was, we'd expect data usage to be as high as the virtual assistants' data consumption.”